This invention relates to a bearing assembly, and more particularly to rotary friction bearing assembly for a roller cutter drill bit.
This invention involves an improvement over the rotary friction bearing assembly for roller cutter drill bits of the type disclosed in co-assigned U.S. Pat. No. 3,917,361, comprising a bearing journal, a roller cutter rotatably mounted on the bearing journal, and a so-called "floating" bushing between the bearing journal and roller cutter which is free to rotate relative to both the journal and the roller cutter. The bushing is of generally annular configuration and is split in the direction of its longitudinal axis to provide a gap enabling the bushing to accomodate thermal expansion of the bushing metal due to heating of the bearing assembly on use of the drill bit.
The engaging surfaces of the bearing members of this bearing assembly are machined to relatively close tolerances to reduce the amount of clearance or play in the bearing assembly. While a certain amount of clearance is needed for relative rotation of the bearing members, clearance in excess of this desired amount leads to shortened bearing life. Heretofore, the desired dimensional tolerance of the bushing could be obtained only by the relatively time-consuming and costly process of machining, as by turning down on a lathe, cylindrical or tubular metal stock and cutting the slit in the bushing after its machining.
Attempts to bend or wind a length of strip material of a thickness and width corresponding to that of the finished bushing around a mandrel to form the bushing proved to be unsuccessful. Because of the elastic deformation properties of the bushing metal, the strip material after being wound into a circular configuration exhibited a tendency to "spring open" (i.e., deviate from a circular configuration) at the gap between the opposing ends thereof. This resulted in these strip metal bushings being out-of-tolerance and thus unusable.